Tutorial - CP 2014

At CP 2014 in Lyon I gave a tutorial
about automated reformulation, with this title and abstract:

Automated Reformulation of Constraint Models in Savile Row

Abstract. Modelling languages such as OPL, MiniZinc
and Essence’ have been and continue to be the focus of considerable research
effort. These languages have several advantages compared to using a constraint
solver directly: they abstract away from solver-dependent details of modelling
to provide the user with a consistent language for multiple constraint solvers;
they typically allow arbitrary nesting of expressions when constraint solvers
do not; and they provide an opportunity for automated optimisation and
reformulation of the model, before it is flattened and specialised for a
particular solver. This tutorial focuses on automated optimisation and
reformulation at the instance level, i.e. after problem class parameters have
been substituted into the model. I also focus on finite-domain integer
constraint problems, although many of the techniques can also be applied to
continuous variables and set variables. I will use Essence’ and Savile Row as
an example language and system.

The first part of this tutorial will be an overview of published reformulations
of constraint models, such as active CSE and constraint aggregation. The second
part will be a description of the internals of Savile Row, with example
problems demonstrating various useful reformulations that it can perform.

Finally, the third part of the tutorial will focus on examples where a sequence
of reformulations leads to a surprising result. One example of this is BIBDs,
where a sequence of three reformulations lead to a model that improves on the
sophisticated model published by Frisch et al (which itself is far better than
the model commonly used in the constraints literature).